# Query Registration

How to register query handlers in dependency injection.

## Basic Registration

```csharp
builder.Services.AddQuery<GetUserQuery, UserDto, GetUserQueryHandler>();
```

**This registers:**
- Handler as `IQueryHandler<GetUserQuery, UserDto>`
- Metadata for endpoint discovery
- Scoped lifetime (default)

## Registration with Validator

```csharp
builder.Services.AddQuery<SearchUsersQuery, List<UserDto>, SearchUsersQueryHandler, SearchUsersQueryValidator>();
```

**This registers:**
- Handler
- Validator as `IValidator<SearchUsersQuery>`
- Metadata

## Bulk Registration

### Extension Methods

```csharp
public static class ServiceCollectionExtensions
{
    public static IServiceCollection AddUserQueries(this IServiceCollection services)
    {
        services.AddQuery<GetUserQuery, UserDto, GetUserQueryHandler>();
        services.AddQuery<ListUsersQuery, List<UserDto>, ListUsersQueryHandler>();
        services.AddQuery<SearchUsersQuery, PagedResult<UserDto>, SearchUsersQueryHandler, SearchUsersQueryValidator>();
        return services;
    }
}

// Usage
builder.Services.AddUserQueries();
```

### By Feature

```csharp
public static IServiceCollection AddOrderQueries(this IServiceCollection services)
{
    services.AddQuery<GetOrderQuery, OrderDto, GetOrderQueryHandler>();
    services.AddQuery<ListOrdersQuery, PagedResult<OrderDto>, ListOrdersQueryHandler>();
    services.AddQuery<GetOrderStatisticsQuery, OrderStatistics, GetOrderStatisticsQueryHandler>();
    return services;
}
```

## Service Lifetimes

### Scoped (Default)

```csharp
services.AddQuery<GetUserQuery, UserDto, GetUserQueryHandler>();
// Handler is Scoped - can inject DbContext
```

### Custom Lifetime

```csharp
// Transient
services.AddTransient<IQueryHandler<GetUserQuery, UserDto>, GetUserQueryHandler>();

// Singleton (not recommended for queries with DbContext)
services.AddSingleton<IQueryHandler<GetUserQuery, UserDto>, GetUserQueryHandler>();
```

## Organization Patterns

### By Domain

```
Extensions/
  UserQueryRegistration.cs
  OrderQueryRegistration.cs
  ProductQueryRegistration.cs
```

### By Type

```
Extensions/
  QueryRegistration.cs
  CommandRegistration.cs
```

## See Also

- [Command Registration](../commands/command-registration.md)
- [Dependency Injection](../../architecture/dependency-injection.md)